The cutting of a hole into a workpiece is a commonly performed machining operation. The development of drills, lubricants, and related techniques for metallic workpieces for hole drilling has been ongoing.
Fiber composite materials are formed of fibers embedded into a matrix, wherein the individual phases retain their respective characters in the composite material. These materials offer good mechanical properties coupled with light weight and are therefore used in a number of aircraft-related applications. Examples of such fiber composite materials are organic-matrix composites such as carbon fibers in an epoxy matrix; metal-matrix composites such as boron fibers in an aluminum-alloy matrix; and ceramic-matrix composites such as silicon carbide fibers in a silicon/silicon carbide matrix, termed a silicon carbide/silicon carbide composite material.
The cutting of holes in such composite materials is often difficult for a number of reasons. The fibers and the matrix usually have different mechanical properties, so that the cutting process is not uniform. The fibers and/or the matrix may be hard and difficult to cut. The anisotropy in the structure may also contribute to difficulty in cutting and also to irregularity of the shape of the hole and its positioning. There is a tendency for the fibers to debond from the matrix as the hole is drilled, so that there is splintering and fraying of the composite material on the sides of the drilled hole and at the front and back faces of the workpiece. This splintering and fraying reduces the mechanical properties of the composite material and can lead to crack initiation and premature failure of the composite material.
A number of techniques have been proposed to drill holes in composite materials. These techniques are operable to varying degrees, but none has been found fully satisfactory in cutting holes in certain types of composite materials such as ceramic-matrix composite materials. There is accordingly a need for an improved approach to the cutting of holes in composite materials. The present invention fulfills this need, and further provides related advantages.